Remove an unnecessary OP_Null in the IN-operator logic. Attempt to clarify

comments explaining the IN-operator code, though it is not clear that the
comments are correct even yet - more work to be done.

FossilOrigin-Name: c11e55fabbc718cb324ecd3540453c25db98f50c

manifest

@@ -1,5 +1,5 @@
-C Clean\sup\sthe\sIN\soperator\scode\sgeneration\slogic\sto\smake\sit\seasier\sto\sreason\nabout.\s\sIn\sthe\sprocess,\simprove\scode\sgeneration\sto\somit\ssome\sunused\sOP_Null\noperations.
+C Remove\san\sunnecessary\sOP_Null\sin\sthe\sIN-operator\slogic.\s\sAttempt\sto\sclarify\ncomments\sexplaining\sthe\sIN-operator\scode,\sthough\sit\sis\snot\sclear\sthat\sthe\ncomments\sare\scorrect\seven\syet\s-\smore\swork\sto\sbe\sdone.
-D 2014-08-01T15:51:36.528
+D 2014-08-01T18:00:24.770
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 5eb79e334a5de69c87740edd56af6527dd219308
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -176,7 +176,7 @@ F src/complete.c dc1d136c0feee03c2f7550bafc0d29075e36deac
 F src/ctime.c 0231df905e2c4abba4483ee18ffc05adc321df2a
 F src/date.c 593c744b2623971e45affd0bde347631bdfa4625
 F src/delete.c bcf8f72126cea80fc3d5bc5494cf19b3f8935aaf
-F src/expr.c 1f7fa7ddbdffd89898a3ce5ff1e57d137ec87aa5
+F src/expr.c 45da7f2dd6b5c52b3210387956711d578bdceb37
 F src/fault.c 160a0c015b6c2629d3899ed2daf63d75754a32bb
 F src/fkey.c 8545f3b36da47473e10800ea4fb0810fd4062514
 F src/func.c 3bc223ea36cd29a91c481485343d0ee4257ab8dc
@@ -283,7 +283,7 @@ F src/update.c 01564b3c430f6c7b0a35afaf7aba7987206fa3a5
 F src/utf.c a0314e637768a030e6e84a957d0c4f6ba910cc05
 F src/util.c 3076bdd51cdbf60a6e2e57fada745be37133c73e
 F src/vacuum.c 3728d74919d4fb1356f9e9a13e27773db60b7179
-F src/vdbe.c 115e08834b883964d9a480f685d8601826c5792a
+F src/vdbe.c b9e6866e43a61ca4080410f27c4bb52823495186
 F src/vdbe.h c63fad052c9e7388d551e556e119c0bcf6bebdf8
 F src/vdbeInt.h f5513f2b5ac1e2c5128996c7ea23add256a301df
 F src/vdbeapi.c 24e40422382beb774daab11fe9fe9d37e8a04949
@@ -1185,8 +1185,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 9abcf2698c09f4f6a44a68e74f9f6b538f3253d6 e13175d3579e1045165bab091b3b28951d691704
+P 7c6fbcfe6ed5739e8e4639b7b123fbf9828cbfc0
-R b49330a02feffafe84f051ae1dbb9076
+R 76f22de612006799aae8055deaa164fe
-T +closed e13175d3579e1045165bab091b3b28951d691704
 U drh
-Z e21436d3fd2e7daacda65f50d724cf15
+Z ebc1ba4c7f530e221b3bc2fcb7e1119a

manifest.uuid

@@ -1 +1 @@
-7c6fbcfe6ed5739e8e4639b7b123fbf9828cbfc0
+c11e55fabbc718cb324ecd3540453c25db98f50c

src/expr.c

@@ -1525,29 +1525,34 @@ int sqlite3CodeOnce(Parse *pParse){
 **
 ** When the b-tree is being used for membership tests, the calling function
 ** might need to know whether or not the RHS side of the IN operator
-** contains a NULL.  If prNotFound is not NULL and 
+** contains a NULL.  If prRhsHasNull is not a NULL pointer and 
 ** if there is any chance that the (...) might contain a NULL value at
 ** runtime, then a register is allocated and the register number written
-** to *prNotFound. If there is no chance that the (...) contains a
+** to *prRhsHasNull. If there is no chance that the (...) contains a
-** NULL value, then *prNotFound is left unchanged.
+** NULL value, then *prRhsHasNull is left unchanged.
 **
-** If a register is allocated and its location stored in *prNotFound, then
+** If a register is allocated and its location stored in *prRhsHasNull, then
-** its initial value is NULL.  If the (...) does not remain constant
+** the value in that register will be:
-** for the duration of the query (i.e. the SELECT within the (...)
-** is a correlated subquery) then the value of the allocated register is
-** reset to NULL each time the subquery is rerun. This allows the
-** caller to use vdbe code equivalent to the following:
 **
-**   if( register==NULL ){
+**          0      if the (...) contains no NULL values
-**     has_null = <test if data structure contains null>
+**          1      if the (...) does not contain NULL values
-**     register = 1
+**       NULL      if we do not yet know if (...) contains NULLs
+**
+** If the (...) does not remain constant for the duration of the query
+** (i.e. the SELECT within the (...) is a correlated subquery) then the
+** value of the allocated register is reset to NULL each time the subquery
+** is rerun. This allows the caller to use vdbe code equivalent to the
+** following:
+**
+**   if( r[*prRhsHasNull] IS NULL ){
+**     r[*prRhsHasNull] = <test if data structure contains null>
 **   }
 **
 ** in order to avoid running the <test if data structure contains null>
 ** test more often than is necessary.
 */
 #ifndef SQLITE_OMIT_SUBQUERY
-int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prNotFound){
+int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prRhsHasNull){
   Select *p;                            /* SELECT to the right of IN operator */
   int eType = 0;                        /* Type of RHS table. IN_INDEX_* */
   int iTab = pParse->nTab++;            /* Cursor of the RHS table */
@@ -1621,9 +1626,9 @@ int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prNotFound){
           assert( IN_INDEX_INDEX_DESC == IN_INDEX_INDEX_ASC+1 );
           eType = IN_INDEX_INDEX_ASC + pIdx->aSortOrder[0];
 
-          if( prNotFound && !pTab->aCol[iCol].notNull ){
+          if( prRhsHasNull && !pTab->aCol[iCol].notNull ){
-            *prNotFound = ++pParse->nMem;
+            *prRhsHasNull = ++pParse->nMem;
-            sqlite3VdbeAddOp2(v, OP_Null, 0, *prNotFound);
+            sqlite3VdbeAddOp2(v, OP_Null, 0, *prRhsHasNull);
           }
           sqlite3VdbeJumpHere(v, iAddr);
         }
@@ -1643,9 +1648,8 @@ int sqlite3FindInIndex(Parse *pParse, Expr *pX, u32 inFlags, int *prNotFound){
       if( pX->pLeft->iColumn<0 && !ExprHasProperty(pX, EP_xIsSelect) ){
         eType = IN_INDEX_ROWID;
       }
-    }else if( prNotFound ){
+    }else if( prRhsHasNull ){
-      *prNotFound = rMayHaveNull = ++pParse->nMem;
+      *prRhsHasNull = rMayHaveNull = ++pParse->nMem;
-      sqlite3VdbeAddOp2(v, OP_Null, 0, rMayHaveNull);
     }
     sqlite3CodeSubselect(pParse, pX, rMayHaveNull, eType==IN_INDEX_ROWID);
     pParse->nQueryLoop = savedNQueryLoop;

src/vdbe.c

@@ -2229,13 +2229,13 @@ case OP_Once: {             /* jump */
 **
 ** Jump to P2 if the value in register P1 is true.  The value
 ** is considered true if it is numeric and non-zero.  If the value
-** in P1 is NULL then take the jump if P3 is non-zero.
+** in P1 is NULL then take the jump if and only if P3 is non-zero.
 */
 /* Opcode: IfNot P1 P2 P3 * *
 **
 ** Jump to P2 if the value in register P1 is False.  The value
 ** is considered false if it has a numeric value of zero.  If the value
-** in P1 is NULL then take the jump if P3 is zero.
+** in P1 is NULL then take the jump if and only if P3 is non-zero.
 */
 case OP_If:                 /* jump, in1 */
 case OP_IfNot: {            /* jump, in1 */